Amplifying system



' OCLZO, 1931. 4 SILVA 1,828,688

AMPLIFYING SYSTEM Original Fil ed'May 10. 1929 vPatented 011.20, 1931UNITED STATES. PATENT: OFF-ICE ALBERT DxSILVA, OFIHILADELPHIA,PENNSYLVANIA, ASSIGNOR 'IO A'IWATER KENT MANUFACTURING COMPANY, OFPHILADELPHIA, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA Originalapplication flied m 10, ms,

My invention relates to radio receiving apparatus or the like,utilizingthermionic tubes supplied from a source of fluctuating current,as for example, from a rectifier system through a filter comprising asuitable combination of impedances.

v In accordance with my invention, the field winding of an electro-dynamic speaker is in-' I cluded in circuit in the negatlve conductor of anelectrode current supply and all or any 7 suitable portion of 'the dropof potential acro'ss'the fieldwinding is utilized to bias grid structureof one or more tubes, partlcularly power amplifier tubes requiring highmagnitude of, biasing potential; and more specifically the field windingis included in the negative side or conductor of an alternating currentrectifying and filtersystem, either external to the filter system,or,and

preferably, within the filter system to serve as an impedance'thereof.

This ap lication is a division from my application erial No. 361,910,filed May 10, 1929. i

For an understanding of my invention, reference is to be had to theaccompanying drawin push-pull relation. The primary P1 of movable coil Mof an electrodynamic speaker haying a diaphragm D, actuated by the coilthe transformer T1 is connected at its outer terminals to the anodes aof the tubes V1, V2, and is inductively related to the secondary S1 ofthe transformer which is connected to the' M. Thecondenser K connectedetween the anodes a of tubes V1, V2 cooperates with transformer T1 and eil Cto reduce in amplitude or to cut 0 objectionable highpitched noisesattendant to high amplifica tion, particularly when an electrodynamic 1mnmmc sYsrEim Serial No. 361,910. Divided and this application filedFebruary 85,

Serial No. 518,097. 7 I

speaker is utilized as a sound reproducer. V

The capacity example of the order of .02 mfd.

The input circuit of the tube V may be associated with the outputcircuit of a detector, preferably preceded by one or more radiofrequency amplifier stages to constitute radio receiving. apparatus, orof an audio amplifier tube preceded by a detector and radio frequencyamplifier stages, or the input circuit of the tube V may includephonographic pick-up device.

In Fig. 1, the tube Vamplifies at radio frequency and is coupled to theanode circuit of the detector tube V4 by resistance T3 and condenser C5.Preferably between the input circuit of the detector and an antennapath;

or absorption loop, there may be interpose one-or more stages of radiofrequency amplification. The input circuit of the screengrid amplifiertube V5, preferablytuned, is directly associated with the absorptionpath or there may be interposed one or more additional stages of radiofrequency amplifica tion, and its anode circuit is coupled to the inputcircuit of the detector V4 by transformer T5. The input circuit of thetube V4 is prelfg'ably' tuned, as by variable condenser s The tubes v4.and V5 are provided with" heaters htraversed by current supplied from ofthe condenser may be for the secondary S4 of a power supply transformerT2 to raise the tem erature of the uni-potential cathodes u to e ectemission of electrons. The cathodes f of the tubes V1 and and otherradio frequency amplifier tubes may be of the three-electrode type andutilizing a heavy filament, instead ofa heater and a unipotentialcathode, in whichv event they are connected'in' a manner similar to tubeV4, for example.

The audio frequency variations of current in the primary P of the tube Vact upon the secondary S cumulatively to affect the potential of thegrids g of the tubes V1, V2, i. e., the o'rids are ofopposite-"instantaneous polarities. The amplified current variations inthe primary P1 of the output transformer T1 are impressed upon thesecondaiiiy S1 thereof in their efiect upon the secondary S1, and billand traverse the, movable coil disposed in ance out.

the magnetic'field of winding F to effect reproduction of sound. I. Theprimary P2 of t ansformer T2 sup- I pl gcurrent to'the several electrodecircuits the thermionic tubes is adapted to be energized from anysuitable source, as from line conductors for current of ordinarycommercial frequency, by insertion of plug 1 into a socket receptacle orthe like, not shown.

'- The terminals of the t'ransformer'secondary S2 are connected to asuitable rectifier, specifically to the anodes a of the .full waverectifier tube V3 whose filament or cathode f is heated b currentsupplied from the secondary S3 0 transformer T2. The negative conductor4 of the rectifier system is connected to a midpoint of the splitsecondary S2 and the positive conductor 5 is cofiiecte to the cathode fof the rectifier m o D 1 field coil F of the dynamic s eaker andcondensers C1, C2 and C3. Wln e a two section filter is shown, insofaras certain aspects of my invention are concerned a smaller or greaternumber of filter sections may be utilized. The field coil F of thespeaker being of large inductance, is effective as a filter choke andreplaces an impedance having solely that function. The anode of the tubeV, and of the preceding tubes including radio frequency amplifier tubesof the specific arrangement shown, is connected to the terminal ofinductance L2 remote from the rectifier V3, that is, to point p of thefilter network, and the anodes a, w, of the tubes V1,

40 V2 are connected to a point p1 of the filter network intermediate theinductances L, L2.

1 The potential of the point p1 is substantially greater than that ofthe point p because of 7 .'tlie high direct current resistancegf the in-.ductance-L2. The potential applied to the anodes a, a, of thepow'ertubes V1, V2, is-

therefore suitably high, without, subjecting the rectifier to highvoltages. Although the potential pf point pl-varies somewhat more thanthat of the point p of the filter, nevertheless as the tubes V1, V2 arenot followed by a subsequent stage or stages of audio amplification, thehum of line frequency or a inultiple thereof reproduced .by the loudspeaker is l not noticeably or appreciably increased. Additionally asthe field winding is in the second filter section, there is negligiblysmall difierence of alternating potentialof the frefen quency (ormultiple thereof) of the powersupply across its terminals.

urther in the push-pull arrangement shown as the connection from'thepoint p1 is to a midpoint of the primary P1 the riodic 06 variations ofsupply currentare erentlal proximately somewhat less than Hithertoforeand particularly in apparatus in which the tubes were supplied fromalternating current, grid biasing potential has been commonly producedby utilizing the voltage drop across resistance traversed by the anodecurrent. This arran ement reduces the volta e at the anode of t e tubeand is uneconomica andimpractical with power tubes receiving highnegative bias, because of excessive demand upon the rectifier and/orfilter system.

In accordance wlth oneaspect of my invention the field winding F of thedynamic speaker included in the negative conductor 4 of the power supplyis traversed by t e total'anode current of all tubes and a whole or apart of the drop of potential across the windin is utilized to bias thegrids g of the 83 tubes V1, V2, V4 and V5. The direct current resistanceof the field winding is of The rectified current is smoothed by a filternetwork comprised by the inductances L1, L2,

such value that for normal demand upon the rectifier filter systeni,the-voltage dro across the winding is equal to or in excess 0 thereguired grid bias for the power tubes V1, V2,

or example the total drop maybe in excess of volts. Preferably as shownthere is a conductive impedance R,specifically a resistor, of suitablyhigh magnitude of resistance as for example 17,500 ohms connected inshunt to the field coil F. The use of the potentiometer resistance R, orequivalent, avoids the necessity of tappin' the winding F, (Fig.2)although it will understood my invention is not limited to the use ofresistance R. s The impedances of the field winding F and of theresistance B should be so proportioned that the filtering action of thefield windin F is not seriously impaired. For example, t e value ofresistance above given is suitable for a speaker having an lmpedance of6000 ohms' at 60"cycles an direct c'urrentresistanceof about 1100 ohms.The potentiometer arrangement has the ar vantage of insuring goodreproduction in the event of heavy signals-and consequent flow of gridcurrent. I

A conductor 6 is connected between the midpoint of the secondary S ofthe input transformer T of the push-pull stage and a suitable point onthe potentiometer resistance R. i As the type tubes utilized in thespecific circuit shown, are used, with e 50 volt grid bias, the gridconnection 6 is to a oint apalf way across R from its more positive end,that is the grounded terminal. For other types of power tubes, or forother tubes of the same apparatus, connections from the grids may' bemade to resistance R intermediate its ends,

or to its terminals to points of potentials corresponding to the desiredbiases. Furthermore the potential drop ma be utilized for other:purposes, forexamp e, in the automaticcontrol of volume of reproduction"as 1 audio frequency. As the grid biasing voltgages are small comparedto that required for -the tubes V1 and V2, it may be obtained withoutserious reduction of anode voltage by this known arrangement abovereferred 4 to. The ower tubes V1, V2 are operated at much hig er platevoltages and require grid biasing potentials many times larger than thatsuitable for the tubes V, etc. In the arrangement described the gridbiasing potential and plate current for the tubes V1, V2 areeconomically obtained, as the voltage drop across a rearranged filterinductance, specifically field winding F is utilized for grid-biasingpurposes, thus'making available a greater output, or the same outputwith reduced input, smaller transfdrmers, etc. The arrangement shown anddescribed has resulted in an increase of as much as,25% 1n the effectiveoutput of the rectifier-filter system. i

In radio receiving apparatus utilizing the arrangement thus fardescribed, within a short time after closing ,of switch 2 eflectingsupply of power to the electrode circuits of the tubes, there isexperienced a transient,

disagreeable squawk. .It was finally determined that the'temporary butobnoxious disturbance resulted from the unequal rates of impedance ofthe tubes V1, V2 as their re spective filaments approached operatingtemperature, and/or because of the connection from the'point pl of thefilter to the anodes a of the tubes V1, V2. This'trouble some effect wasovercome by connecting the condenser C4 ofsuitable capacity, for example.1 mfd across the connections to the input electrodes of the tubes, thatis in shunt to the portion of the resistanceR common to the anode andgrid circuits of the tubes V1- and V2.

The amplitude of reproduction may be controlled by adjustment of contact8 along the potentiometer resistance R3 connected between positive.terminal .p of the filter and ground to vary the potential ofthe screengrid sg of the amplifier tube V5.

Referring to Fig. 2, the field winding F is outside of the filternetwork, but is included r fifl in the negative conductor 4 that thehigh ,drop of potential across it maybe utilized tobias the grids oftubes of associated apparatus. If the source of current delivers pureirect--current, as for example when a battery veither, primary orsecondary n character is 'used, the filter iinpedances may be entirelyomitted.

In the modification of my invention shown I in Fig. 3, the grid biasingresistances 1, W1

and 72 are dispensed with and connection is made from therespectivecathodes u-to suitable points .on the several potentiometer resistancesR1, R2, etc. connected in shunt to resistance R and field windingF. Itwill be understood that this shunt arrangement may also be utilized whenthe field winding F is outside of the filter, if used, as in themodification of Fig. 2. v

1 ,In another aspect of my invention, by disposition of the fieldwinding F of the speaker in the negative conductor of-the anode supplycircuit, there is relatively low difference of potential between thespeaker and ground which avoids the possibility, for example, ofdangerous shocks in the event of connection between the winding F andmetallic housing structure of the speaker. Further to increase thefactor of safety, the circuit including the secondary S1 of transformerT1 and the movable coil Mi may be grounded as indicated. v

What I claim is:

1. A system comprising an electrodynamic speaker having a movab e coiland a field winding, a thermionic tu e, means to effect flow of currentin a path including. said field winding and tube electrode structure inseries, a condpctive impedance of high resistance in shunt to saidwinding, and connections from tube input electrodes to points, at leastone of which is intermediate the terminals of said I namic speakerhaving a movable coil trav ersed by currents of audio'frequ my and afield winding energized by direct current traversing electrode circuitsof 'said tubes,

and conductive impedance of high resistance in shunt to saidfield'winding, a connection from one terminal of said field winding tocathode structure of said tubes, and connections from the grids of saidtubes to. points of said impedance of potential suitably differing inpolarity and magnitude from the potential of said terminal. I r

3. A system comprising a thermionic tube able coil and a field winding,a current source fortube electrode structure comprising a filter networkincluding said field winding wholly in the negative conductor thereof, aconnection'from tube cathode structure to a 'fpToint in said filter;network, and a connection om the grid structure of said tube to' a sec-'ond pomt in said-network more negative than and an electrodynamicspeaker having a movtrode structure comprising a filter network saidfirst int and havin a potential intermediate t e potentials theterminals of saidwinding; i

4. A system comprisin an electrodynamic speaker having amova le coilanda field winding, a power amplifier tube'r uiring high grid bias, acurrent source for tu elecincluding all of said field winding in thenegative conductor thereof, and connections from tube input electrodesto points 1n the filter network of substantial potential differencederived from andless than -the drop of. potential across said fieldwinding.

an electro-dynamic 1e coil and a Ifield 5. A system comprising speakerhaving a mova winding, a thermionic tube, a current source for tubeelectrode structure comprising afilter network including said fieldwinding, a conductive impedance of high resistance in shunt to saidfield winding, a connection from tube cathode structure to a point ofsaid impedance, and a connection from tube grid struc-' ture to a secondpoint of said impedance more negative than said first point.

6. A system comprising an electrodynamic speaker 'having a movable coiland a field winding, a thermionic tube, a current source for tubeelectrode structure comprising a filter network including said fieldwind ng, a resistor-in shunt to said field winding, a connection fromtube cathode structure to a terminal of said field winding, and aconnectionfrom tube grid structure to an intermediate point of saidresistor,

7. A system comprising an electrodynamic speaker having a movable coiland a field winding, cascaded thermionic tubes including a power amlifier tube, a current source for tube electr e structure, amulti-section v filter including serially connected conductive terminalof 'said filter,

from ,and less impedances in'the positive conductor and said fieldwinding in the negative conductor, a connection to power ampllfier anodestructure from a point between serially connect-' ed impedances, aconnection to anodestrucv ture of another said idlbe from the outputconnections between ower amplifier input electrddes and points in thefilter of ntial' difl'erence derived.

across said field winding-,and a by-pass condenser connected betweensaidbOnnectIons.

8. A stem comp an electrodynannc speaker aving a'mova le' coil andafield winding, cascaded thermionic tubes including a wer am lifiertube, a current source for tu electro e structure, amulti-section filterincluding serially connected conductive i impedances in the positiveconductor and said field winding in'the negative conductor, a connectionto power amplifier anode struc-' ture from a point between seriallyconnected impedancies, a co ection' to anode structure of another ofs'ai tubes from the output teran the drop of potential tions betweenpower amplifier input-elechides and points of said resistance. of:substantially difierent potential, and a by-pass condenser connectedbetween said last named connections; c

9. A system comprisi an electrodynamic speaker havin' a mova 1e coil anda field winding, a pus geull audio amplifier utilizthermionidtu ab ecoil in the out ut circuit thereof, a current source for tu e electrodestructure, a filter network including said field winding in the negativeconductor thereof a, otentiometer im edance in shunt to said eldwinding, an connections from the grids and cathodes of said tubes topoints of said impedance between which there exists difierence ofpotential resulting from flow of current through said field winding.

s and including said mov- 10. A system comprisin an electrodynamfilternetwork including said field winding in.

thenegative conductor thereof, a potentiometer impedance in shunt tosaid field winding,

connections from the grids and cathodes of said tubesto points of saidimpedance between which there exists difi'eren'ce of potensaid fieldwinding, and a by-pass condenser between said connections.

11. A system comprising thermionic tub/es a current source therefor, amulti-section filter associated therewith, a conductive impedance in thenegative conductor of a filter section remote from said current source,and connections from tube input electrodes to points in the filternetwork of otential dif ference derivedfrom and less t an the dro ofpotential; across said conductive impe ance. v

12. A system comprising a thermionic tube having an anode, a cathode anda control electrode, a speaker having a field winding, a

sourceof current for the anode circuit ofsaid tube, said field windingtraversed by one of which is intermediate the terminals of saidimpedance, between-whichexists substantial difference of potential;

13. Thecombinationwith a system com-- prising a thermionic tube havlngan anode, a v

cathode and a controlelectrode, a source oi uni-directional current .forthe anode circuit of said .tube, a field winding of a speaker traversedby current in said anode circuit .tial resulting from flow of currentthrough from; said source,of means for biasing the, 15

I control electrode of said tube negatively with respect to its cathodecomprising a conductive impedance in shunt with said field wind- 7 ing,and connections from said control electrode and ,cathode to ointsbetween which exists a substantial dlflerence of potential, one of saidoints disposed intermediate the terminals ot said impedance. I 14. Asystem comprising cascaded ther- 10 mionic tubes, one of which am lifiesat radio frequency and another of w ich amplifies at audio frequency, anelectrodynamio speaker having a field winding traversed by directcurrent'traversing the anode circuits of said tubes, a plurality ofimpedances in shunt to said field winding, and connections from pointsintermediate terminals of said impedances to grids of different tubes,said points being more negative than said cathodes, and

. 0 the potential difi'erence between said points and said cathodesbeing, less than the total fall of potential across said field winding.

- ALBERT D. SILVA.-

